To reduce the cost per page of printing, commercial grade inkjet printers are designed so that the print heads are not disposed of when the ink runs out. Instead, ink is supplied to the print heads by a pump mechanism from disposable inkbags.
One form of conventional pump mechanism includes a series of lifters (one per bag) that push against an associated diaphragm of a refill chamber in the disposable inkbag. A one-way valve divides the inkbag into a main reservoir and the refill chamber. The pressure of the lifter on the diaphragm causes the ink in the refill chamber to be pressurized and this forces ink to flow out to the associated pen via an ink tube. However, when the refill chamber is empty, no resistance is provided to the lifter by the ink and thus the lifter is free to move to a height that is known as the “out of ink height”. When the lifter reaches the “out of ink height”, a sensor is triggered by a component associated with the lifter. This in turn provides a signal to a user that the inkbag refill chamber is out of ink. Typically, the sensor is an optical sensor.
One of the requirements of the above arrangement is that there is a need to accurately signal when the refill chamber is empty. It has been found however that due to the various parts between the lifter and the component that actually triggers the sensor, there can be a lot of inherent error in the mechanism and thus the sensor may not be properly triggered. The errors may be due to manufacturing tolerances of the components, assembly errors and wear and tear over time. Additionally, optical sensors can have variations in their diode location, which in turn results in variations in the trigger point.
To overcome the above mentioned problems it has been necessary to adjust the “out of ink height” of the pump mechanism. This requires manual adjustment of the height of each lifter of the inkjet printer which is a time consuming and tedious procedure incurring extra expense and process time.
The present invention seeks to provide an improved mechanism for signalling that the refill chamber of the disposable inkbag in inkjet printer is empty.